Filtering devices that are percutaneously placed in a vena cava have been available for many years. A need for filtering devices arises in trauma patients, orthopedic surgery patients, neurosurgery patients, or in patients having medical conditions requiring bed rest or non-movement. During such medical conditions, the need for filtering devices arises due to the likelihood of thrombosis in the peripheral vasculature of patients wherein thrombi break away from the vessel wall, risking downstream embolism or embolization. For example, depending on the size, such thrombi pose a serious risk of pulmonary embolism wherein blood dots migrate from the peripheral vasculature through the heart and into the lungs.
A filtering device can be deployed in the vena cava of a patient when, for example, anticoagulant therapy is contraindicated or has failed. Filters have been used or considered in preoperative patients and in patients predisposed to thrombosis which places the patient at risk for pulmonary embolism.
In certain situation, it is desirable to remove a vena cava filter from the patient body. After deployment of a filter in a patient, however, proliferating intimal cells begin to accumulate around the filter struts which contact the wall of the vessel. Additionally, filters may become off-centered or tilted with respect to the hub of the filter and the longitudinal axis of the vessel in which it has been inserted. As a result, the filter including the hub and the retrieval hook may engage the vessel wall along their lengths and potentially become endothelialized therein. Under such conditions, it is very difficult if not impossible to engage the retrieval hook in a known manner with a snare.